1. Field of the Invention
This invention relates to a method for bending tubular bodies or pipes as well as to a device or equipment for carrying out such method.
2. Description of the Prior Art
As is already well known, when forming pipe-lines for conveying fluids through tubular bodies, the pattern thereof is usually bent, since already existing and non removable obstacles and obstructions must be avoided (e.g. when conveying natural gas the pipe-lines must avoid houses, roads, rivers, various structures and the like, while in machine tools, the obstacles represented by control members, traverse runs of movable components and so on must be avoided).
Thus, the path of tubular bodies or pipes by which fluids are conveyed consists of a series of broken lines and includes elbows having preestablished radii curvature radii. Elbows having a very small radius of curvature cannot be obtained by pipe deformation and consequently when such small radius elbows are required, cast hollow bodies, which can have even a zero radius of curvature or welded elbows as obtained by hot forming an initially straight pipe with a minimum radius of curvature having the same order of magnitude as the pipe radius are to be used. Only for larger radii of curvature it is possible to obtain elbows by cold forming the same pipe as utilized for the pipelines.
These limits of the cold bending procedures are due to the working principle inherent in same procedures, since:
1. Only the pipe portion of the elbow is deformed.
2. The forming operation is carried out by mutual rotation of adjacent sections of the pipe length which is bent.
In all already known cold bending procedures, the minimum radius of curvature is a function both of the cross section of pipe to be bent (a function of the diameter in the case of cylindrical pipes), and of the pipe wall thickness, as well as of the material ductility or the ultimate elongation.
In fact, during the bending operation, wherein a mutual rotation of the deformed pipe sections occurs, all points of the outer side of the elbow are drawn away from each other as a consequence of stretching the pipe material, while all points of the inner side of the elbow are brought nearer to each other by compression, until eventually curling of the material is caused. When the pipe material to be stretched cannot be supported by a core, flattening of the pipe may take place, while curling occurs when the material of the inner side of the elbow cannot be kept stretched.